The 1990 Clean Air Act Amendments require major sources of air emissions to limit the discharge of NO.sub.X. NO.sub.X is present in the flue gas emitted from combustion processes. Therefore, cost-effective methods for controlling NO.sub.X are of significant interest.
Selective Catalytic Reduction (SCR) catalysts for NO.sub.X removal are known in the art. Conventional NO.sub.X SCR catalysts require large amounts of catalyst and the flue gas stream to be at relatively high temperatures (between approximately 300 to 400.degree. C.) in order to have sufficient activity for effective NO.sub.X reduction. In such schemes, ammonia is also added as a reducing agent.
There are ongoing efforts to develop low temperature catalysts for applications between approximately 100 to 250.degree. C. Unfortunately, these low temperature catalysts are sensitive to high SO.sub.X, concentrations in the flue gas. There are also NO.sub.X SCR catalysts being developed that are reagentless, so, for instance, ammonia is not required as a reducing agent. These catalyst systems can benefit from the imposition of additional and alternative activating agents to the catalyst so that they can operate at lower temperatures, be less sensitive to poisoning agents, and more reactive without the addition of chemical agents.
In view of the foregoing, it would be highly desirable to provide an approach to enhance NO.sub.X removal. Ideally, the technique would reduce the amount of catalyst needed, or would operate at relatively low temperatures, or reduce the amount of required chemical reducing agents.